Sheet feeding device and image forming apparatus

ABSTRACT

The present invention relates to a sheet feeding device includes a sheet tray  2  to place sheets thereon, a nozzle  9  which blows air onto the sheets supported by the sheet tray  2 , a conveyance belt  10  to adsorb and convey a sheet floated by blowing air by the nozzle  9 , a pulling roller pair  16  which is arranged on a downstream side of the conveyance belt in a sheet conveyance direction and conveys the sheet conveyed by the conveyance belt  10 , and a conveyance guide  17  which guides the sheet conveyed from the conveyance belt  10  to the pulling roller pair  16 . The conveyance guide  17  has slope portions  17   a,    17   b  which are sloped from an upstream side in the sheet conveyance direction to the downstream side to extend from a central portion in a sheet width direction perpendicular to the sheet conveyance direction to both the end portions.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet feeding device including an air paper-feeding mechanism which adsorbs an uppermost sheet of a placed sheet stack on a conveyance belt to separately feed the sheets.

2. Description of the Related Art

Some conventional image forming apparatus such as a printer or a copying machine has a sheet feeding device which blows air on an end portion of a sheet stack stored in a sheet storing portion to loosen the sheets and adsorbs the uppermost sheet of the loosened sheets by a conveyance belt to convey the sheets one by one. An example of the sheet feeding device will be described below with reference to FIG. 10. As shown in FIG. 10, air is blown from a loosening nozzle 101 and a separating nozzle 102 onto an end portion of a sheet stack stored in a sheet storing portion 100 to float a plurality of sheets which constitute an upper portion of the sheet stack to loosen the sheets. After the sheets are loosened, an uppermost sheet is adsorbed on a conveyance belt 103 and separated, the conveyance belt 103 is rotated and sent to a pulling roller pair 105 in the downstream side while being guided by a conveyance guide 104. In this manner, the sheets can be reliably separated from each other and fed one by one. For example, this technique is disclosed in Japanese Patent Application Laid-open No. 7-196187.

However, in the sheet feeding device which adsorbs a sheet on the conveyance belt 103 to convey the sheet, a portion of the sheet which is not adsorbed by the conveyance belt 103 is hanged down, so that defective conveyance may occur. This phenomenon will be described below with reference to FIGS. 11 and 13.

FIG. 11 is a side view (view on an arrow X in FIG. 10) obtained by viewing the device shown in FIG. 10 from the left side (upstream side in a sheet feeding direction). Central portions of floated sheets 106A and 106B in a width direction perpendicular to the sheet conveying direction are sufficiently floated by air blown from the loosening nozzle 101. However, both the end portions of the sheet in a direction of sheet width are hanged down because the end portions cannot be floated. In particular, the uppermost sheet 106B which has been adsorbed by the conveyance belt 103 has a most conspicuous level difference (level difference is indicated by B-P in FIG. 11). This level difference increases in proportion to an increase in sheet size or a reduction in sheet rigidity.

FIG. 12 is a front detail view showing an air-blown part in FIG. 10. In order to give the uppermost sheet 106B adsorbed on the conveyance belt 103 to pulling roller pair 105 as quickly as possible, the conveyance belt 103 and the pulling roller pair 105 are arranged to be close to each other. In such a small space, since the sheet 106B fed while having the above-described level difference is received, a steep slope is formed on the conveyance guide 104.

When feeding is started, as shown in FIG. 13, a forward end portion of the sheet 106B adsorbed on the conveyance belt 103 is caught by the steep slope of the conveyance guide 104, the sheet 106B may climb the slope of the conveyance guide 104 while curling up. In this state, when the sheet is guided between downstream guides or guided to the pulling roller pair 105, a corner of the sheet 106B folds to cause paper jam in sheet conveyance.

If the curling-up of the sheet is eliminated in midstream, the sheet delays due to conveyance resistance generated between the sheet and the conveyance guide 104 on a side on which the curling-up occurs, so that the sheet may be skew-fed. At this time, an image forming apparatus may be deteriorated in accuracy to the sheet, or paper jam may be caused.

SUMMARY OF THE INVENTION

The present invention is made in consideration of the above circumstances. It is an object of the present invention to provide a sheet feeding device which can reliably convey a sheet even if a level difference is generated between a central portion of the sheet in a direction of width and an end portion of the sheet when the sheet is adsorbed and conveyed by a conveyance belt.

In order to solve the above problem, there is provided a sheet feeding device having a mechanism which blows air onto stacked sheets and floats the sheets to loosen the sheets, including:

a sheet storing portion to store sheets;

an air blowing portion which blows air onto the sheets stored in the sheet storing portion;

an adsorption/conveyance portion to adsorb and convey a sheet floated by blowing air by the air blowing portion;

a sheet conveyance portion which is arranged on a downstream side of the adsorption/conveyance portion in a sheet conveyance direction and which conveys the sheet conveyed by the adsorption/conveyance portion to the downstream side; and

a conveyance guide which guides the sheet conveyed from the adsorption/conveyance portion to the sheet conveyance portion; and

wherein a conveyance guide has a slope portion which is sloped from the upstream side in the sheet conveyance direction to the downstream side according to extend from a sheet conveyance center in a sheet width direction perpendicular to the sheet conveyance direction to both the end portions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front explanatory view of a conveyance guide.

FIG. 2 is an upper explanatory view of the conveyance guide.

FIG. 3 is an explanatory view showing a state in which a hanged-down sheet is guided by the conveyance guide.

FIG. 4 is an explanatory view showing a state in which the hanged-down sheet is guided by the conveyance guide.

FIG. 5 is a schematic sectional view for explaining an image forming apparatus having a sheet feeding device.

FIG. 6 is a schematic sectional view for explaining the sheet feeding device.

FIG. 7 is a schematic sectional view for explaining the sheet feeding device.

FIG. 8 is a schematic sectional view for explaining the sheet feeding device.

FIG. 9 is a partial sectional view for explaining an air paper-feeding mechanism.

FIG. 10 is a schematic view for explaining a conventional sheet feeding device.

FIG. 11 is a view for explaining a state in which a conventional sheet is guided.

FIG. 12 is a view for explaining a state in which a conventional sheet is guided.

FIG. 13 is a view for explaining a state in which a conventional sheet is guided.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A sheet feeding device according to an embodiment of the present invention and an image forming apparatus including the sheet feeding device will be described below with reference to the accompanying drawings.

[Entire Configuration of Image Forming Apparatus]

An entire configuration of the image forming apparatus will be described below together with an image forming operation.

FIG. 5 is a schematic sectional view for explaining an image forming apparatus having a sheet feeding device. The image forming apparatus according to the embodiment, as shown in FIG. 5, a sheet feeding device A is arranged in a lower part of an image forming apparatus main body (to be referred to as an apparatus main body hereinafter), an image forming portion B which forms an image on a sheet fed from the sheet feeding device A is arranged above the sheet feeding device A. An image reading portion C which conveys an original, optically read information of the original, and converts the information into a digital signal to obtain an image signal is arranged on an upper portion of the apparatus main body.

In image formation, an image signal read by the image reading portion C is transmitted to the image forming portion B serving as an image forming means, and an image is formed on the sheet on the basis of the signal. The image formation in the embodiment is of electrophotographic type. More specifically, when the image forming signal is input, a photosensitive drum 50 rotates, and a surface of the photosensitive drum 50 is electrically charged by a charger 51. A laser beam from a laser scanner 52 is irradiated on the surface-charged photosensitive drum 50 on the basis of the read image signal, and an electrostatic latent image is formed on the photosensitive drum 50. The electrostatic latent image on the photosensitive drum 50 is developed with toner and then made visual image.

On the other hand, in synchronism with the formation of the toner image, a sheet supplied from a sheet feeding device A (will be described later) is conveyed between the photosensitive drum 50 and a transfer charger 54. The toner image on the photosensitive drum 50 is transferred on the sheet by bias application to a transfer charger 54. The sheet on which the toner image is transferred is conveyed to a fixing unit 55 and heated and pressured to permanently fix the toner image on the sheet. Thereafter, the sheet is discharged to a discharge tray 57 by the discharge roller pair 56.

[Sheet Feeding Device]

A configuration of the sheet feeding device A according to the embodiment will be described below together with a sheet separating/feeding operation.

FIGS. 6 and 7 are schematic views for explaining a sheet feeding device according to the embodiment. The sheet feeding device A has an air paper-feeding mechanism which blows air onto sheets to loosen the sheets and adsorbs an uppermost sheet on a conveyance belt to convey the sheet.

In FIG. 6, a sheet storing portion 1 to store sheets includes a sheet tray 2 on which sheets are supported, a rear-end regulating plate 3 which regulates an upstream side of a sheet in a sheet conveyance direction (to be simply referred to as an “upstream side” hereinafter) and a side-end regulating plate 4 which regulates a sheet in a sheet width direction perpendicular to the conveyance direction. The rear-end regulating plate 3 and the side-end regulating plate 4 are designed such that the positions of the rear-end regulating plate 3 and the side-end regulating plate 4 can be arbitrarily changed. The sheet storing portion 1 is supported by a slide rail 5 such that the sheet storing portion 1 can be inserted into or pulled from the apparatus main body.

In FIG. 7, a user draws the sheet storing portion 1, sets a sheet stack on the sheet tray 2, and loads the sheet storing portion 1 into the apparatus main body again, and the sheet tray 2 rises by a drive means (not shown) in a direction of an arrow A in FIG. 7. The sheet tray 2 stops at such a position that an uppermost sheet of the sheet stack has a preset distance B to an adsorption/conveyance belt 10 and is prepared for a feeding signal.

FIGS. 8 and 9 are partial sectional views showing an air paper-feeding mechanism.

As shown in FIG. 8, a separating fan 6, a separating duct 7, a loosening nozzle 8, and a separating nozzle 9 which constitute an air blowing portion which blows air onto sheets stored in the sheet storing portion 1 are arranged near a downstream of the sheet storing portion 1 in a sheet conveyance direction side (to be referred to as a “downstream side” hereinafter).

In the air blowing portion, when a feeding signal is detected, the separating fan 6 operates to draw air in a direction of an arrow C in FIG. 8. The air is blown from the loosening nozzle 8 and the separating nozzle 9 onto the sheet stack in directions of arrows D and E in FIG. 8, respectively, through the separating duct 7. When the air is blown onto an end portion of a sheet S, several upper sheets S1 of the sheet S are floated and loosened as shown in FIG. 8.

On the other hand, an adsorption/conveyance portion to adsorb and convey an uppermost sheet of the floated sheets by the air blown by the air blowing portion is arranged above the sheet stack. This adsorption/conveyance portion is arranged such that an endless conveyance belt 10 having sucking holes 10 a (see FIG. 2) is hooked on a drive roller 11 and a driven roller 12 to make it possible to rotate the conveyance belt 10. In the adsorption/conveyance portion, an adsorption fan 13 is arranged. The adsorption fan 13 is operated to blow air out, so that an uppermost sheet S2 of the sheet stack is adsorbed on the conveyance belt 10. In a duct 14 of the adsorption fan 13, an adsorption shutter 15 is arranged. The adsorption shutter 15 is opened or closed to control sheet adsorption or non-adsorption on the conveyance belt 10.

Immediately after the sheets are floated by the air blown by the air blowing portion, the adsorption shutter 15 is still closed. When floating of the sheets S1 becomes stable a predetermined period of time after a feeding signal is detected, as shown in FIG. 9, the adsorption shutter 15 is rotated in a direction of an arrow G. In this manner, a suction force (negative pressure) is generated from the suction holes formed in the conveyance belt 10 in a direction of an arrow H to adsorb the uppermost sheet S2. In this state, when the drive roller 11 is rotated, so that the sheet can be conveyed while being adsorbed on the conveyance belt 10.

On the downstream side of the conveyance portion, a pulling roller pair 16 serving as a sheet conveyance portion which conveys a sheet conveyed by the conveyance belt 10 is arranged. The sheet adsorbed and conveyed by the adsorption/conveyance belt 10 is sent by the pulling roller pair 16 toward the downstream side and conveyed to an image forming portion.

[Conveyance Guide]

In the sheet feeding device A according to the embodiment, a conveyance guide 17 which guides a sheet conveyed from the conveyance belt 10 to the pulling roller pair 16 is arranged. A configuration of the conveyance guide 17 will be described below with reference to FIGS. 1 to 4.

FIG. 1 is a front view (drawing viewed in a horizontal direction perpendicular to a sheet conveyance direction) of the conveyance guide 17 according to the embodiment. The conveyance guide 17 according to the embodiment is different from a conventional conveyance guide 104 (see FIG. 12 having a steep slope. As shown in FIG. 1, when viewed in a horizontal direction perpendicular to the sheet conveyance direction, a guide surface of the conveyance guide 17 is slightly sloped. The conveyance guide 17 is slightly sloped in the drawing since passage of paper is reliably performed such that a front-end portion 17 a near a center of the conveyance guide 17 is lower than paper passage rib surfaces 8 a and 9 a arranged at distal ends of the loosening nozzle 8 and the separating nozzle 9 arranged near a conveyance center. Therefore, depending on a positional relationship between the loosening nozzle 8 and the separating nozzle 9, the conveyance guide 17 may be almost horizontally arranged without being sloped. More specifically, when a vertical level of an end portion of the conveyance guide 17 on the uppermost stream side is set to be lower than a sheet adsorption surface of the conveyance belt 10, even though the conveyance guide 17 is horizontally arranged, a sheet adsorbed and conveyed by the conveyance belt 10 is reliably guided by the conveyance guide 17.

The uppermost-stream-side end portion of the conveyance guide 17 is located on the lower side of the conveyance belt 10 and an upstream side of the downstream-side end portion of the conveyance belt 10. In this manner, a portion of a sheet adsorbed by the conveyance belt 10 can be reliably guided.

FIG. 2 is an upper view of the conveyance guide 17. An upstream-side end portion of the guide surface of the conveyance guide 17, as indicated by an arrow in FIG. 2, constitutes slope portions 17 a and 17 b which are linearly sloped from the upstream side in the sheet conveyance direction to the downstream side according to extend from a central portion in a sheet width direction (sheet conveyance reference) to both side end portions. Since the guide surface of the conveyance guide 17 is slightly sloped as described above, the slope portions 17 a and 17 b of the upstream-side end portion are formed with a slight level difference in the vertical direction.

The conveyance guide 17 is made of steel plates, and the upstream-side end portions of the slope portions 17 a and 17 b are subjected to a bending process such that end portions of the steel plates are bent downward. The slope portions 17 a and 17 b, as will be described later, guides a hanged-down portion of a sheet runs on the conveyance guide 17. However, at this time, in order to reduce a load (friction) generated when the sheet is slid on the slope portions 17 a and 17 b, the bending process is effective. Even the slope portions 17 a and 17 b have simple edges, the effect that causes the sheet to run on the slope portions 17 a and 17 b does not change. However, in this case, debarring or the like must be sufficiently performed to prevent the sheet from jamming. For this reason, as in the embodiment, the bending process is desirably performed.

The slope portions 17 a and 17 b have shapes which are symmetrical about the sheet conveyance center (sheet conveyance reference) in the sheet width direction. The conveyance guide 17 is located such that the end portions of the slope portions 17 a and 17 b are arranged outside a maximum sheet width in which a sheet can be conveyed by the device in the sheet width direction and arranged an upstream side of the pulling roller pair 16.

FIGS. 3 and 4 are views for explaining a state in which a sheet hanged down on both the side-end sides is guided by the conveyance guide 17. As shown in FIGS. 3 and 4, a sheet S2 adsorbed by the conveyance belt 10 is hanged down like a sheet S21 shown in FIGS. 3 and 4 before the sheet S2 is brought into contact with the conveyance guide 17. The sheet S21 is conveyed by the conveyance belt 10, and the front end of the sheet S21 is in point contact with a position of a slope portion 17 a 1 of the conveyance guide 17. At this time, contact positions between the front end of the sheet S21 and the slope portions 17 a and 17 b gradually move outside, and the sheet S21 is lifted up along the slope portions 17 a and 17 b.

More specifically, when the sheet is conveyed, the contact point between the sheet and the slope portion 17 a gradually moves to outer sides 17 a 2 and 17 a 3 of the sheet, and the sheet gradually changes into forms indicated by S22 and S23. That is, the hanged-down portion of the sheet is guided to the downstream pulling roller pair 16 while being lifted up by the slope portion 17 a of the conveyance guide 17. Although the above explanation about only the slope portion 17 a which is one of the slope portions is performed. However, a sheet is similarly guided by the slope portion 17 b serving as the other slope portion. As a result, even a hanged-down sheet is guided without being bent at the front end to run on the conveyance guide 17. For this reason, even a sheet which is fed while being hanged down can be conveyed to the image forming portion without causing paper jam.

In the embodiment, since the slope portions 17 a and 17 b have shapes which are symmetrical about the sheet conveyance center in the sheet width direction, a load generated when the hanged-down sheet runs on the conveyance guide 17 is horizontally symmetrical. For this reason, the sheet is conveyed without skew feeding.

A conventional conveyance guide guides a sheet such that a front end of the sheet adsorbed and conveyed by the conveyance belt is in line contact with the guide. On the contrary, the conveyance guide 17 according to the present invention guides a sheet such that the front end of the conveyed sheet is in point contact with the slope portions 17 a and 17 b. For this reason, in the conventional conveyance guide, a sheet curls when the sheet is guided because a resistance applied to the front end of the sheet is large. However, in the conveyance guide according to the embodiment, since a sheet and the guides are in point contact with each other, a resistance of the front end of the sheet against the guide is low, and the sheet is smoothly guided. Therefore, in the conveyance guide of the embodiment does not cause a defect unlike a conventional conveyance guide.

The sheet feeding device according to the embodiment is particularly effective in an environment in which a thin and large-size sheet having low rigidity or a wet sheet largely hanged down is used.

In the embodiment, the slope portions 17 a and 17 b of the upstream-side end portion of the conveyance guide 17 have straight shapes. However, the present invention is not limited to the shapes, and the slope portions 17 a and 17 b may be curved in a concave shape or a convex shape.

This application claims the benefit of priority from the prior Japanese Patent Application No. 2006-085121 filed on Mar. 27, 2006 the entire contents of which are incorporated by reference herein. 

1. A sheet feeding device having a mechanism which blows air onto stacked sheets and floats the sheets to loosen the sheets, comprising: a sheet storing portion to store sheets; an air blowing portion which blows air onto the sheets stored in the sheet storing portion; an adsorption/conveyance portion to adsorb and convey a sheet floated by blowing air by the air blowing portion; a sheet conveyance portion which is arranged on a downstream side of the adsorption/conveyance portion in a sheet conveyance direction and which conveys the sheet conveyed by the adsorption/conveyance portion to the downstream side; and a conveyance guide which guides the sheet conveyed from the adsorption/conveyance portion to the sheet conveyance portion; wherein the conveyance guide has a slope portion which is sloped from the upstream side in the sheet conveyance direction to the downstream side according to extend from a sheet conveyance center in a sheet width direction perpendicular to the sheet conveyance direction to both side end portions.
 2. The sheet feeding device according to claim 1, wherein a level of an upstream-side end portion of the conveyance guide in the sheet conveyance direction is set to be lower than a sheet conveyance surface which is adsorbed and conveyed by the adsorption/conveyance portion.
 3. The sheet feeding device according to claim 1, wherein an end portion of the slope portion of the conveyance guide which is in contact with the sheet is formed symmetrically about a sheet conveyance center in the sheet width direction.
 4. The sheet feeding device according to claim 1, wherein the conveyance guide is arranged almost horizontally.
 5. The sheet feeding device according to claim 1, wherein both end portions of the slope portion of the conveyance guide are located outside a maximum sheet width in which the sheet can be conveyed in the sheet width direction.
 6. The sheet feeding device according to claim 1, wherein the slope portion of the conveyance guide is formed in a straight shape.
 7. The sheet feeding device according to claim 1, wherein the upstream-side end portion of the slope portion in the sheet conveyance direction is subjected to a bending process.
 8. An image forming apparatus including a sheet feeding device having a mechanism which blows air onto stacked sheets and floats the sheets to loosen the sheets, comprising: a sheet storing portion to store sheets; an air blowing portion which blows air onto the sheets stored in the sheet storing portion; an adsorption/conveyance portion to adsorb and convey a sheet floated by blowing air by the air blowing portion; a sheet conveyance portion which is arranged on a downstream side of the adsorption/conveyance portion in a sheet conveyance direction and which conveys the sheet conveyed by the adsorption/conveyance portion to the downstream side; and a conveyance guide which guides the sheet conveyed from the adsorption/conveyance portion to the sheet conveyance portion; and wherein the conveyance guide has a slope portion which is sloped from the upstream side in the sheet conveyance direction to the downstream side according to extend from a sheet conveyance center in a sheet width direction perpendicular to the sheet conveyance direction to both side end portions. 